Gametogenesis Questions in English

(B) The $acrosome$ is a cap-like structure present at the anterior end of the sperm head.
It is derived from the $Golgi$ apparatus and contains hydrolytic enzymes.
The space or the structure located between the $acrosome$ and the $nucleus$ of the sperm head is known as the $perforatorium$.

(A) In the human female,the process of oogenesis begins during embryonic development.
Primary oocytes are formed within the ovary.
These primary oocytes undergo meiosis $I$,which is arrested at the prophase $I$ stage.
Upon reaching puberty,the primary oocyte completes meiosis $I$ to form a large haploid secondary oocyte and a tiny first polar body.
The secondary oocyte then begins meiosis $II$ but gets arrested at the metaphase $II$ stage.
It is at this stage of the secondary oocyte that ovulation occurs,and the ovum is released from the ovary.

(C) The germ cells (primordial germ cells) that give rise to sperm and ovum are derived from the endoderm of the yolk sac during early embryonic development. These cells then migrate to the developing gonads (testes or ovaries). Therefore,the correct origin is the endoderm.

(C) Gametogenesis involves three main phases: the multiplication phase,the growth phase,and the maturation phase.
$1$. Multiplication phase: Germ cells undergo repeated mitotic divisions to increase their number.
$2$. Growth phase: The cells increase in size by accumulating nutrients.
$3$. Maturation phase: The primary gametocytes undergo meiosis (reduction division) to form haploid gametes.
Therefore,meiosis occurs specifically during the maturation phase.

(D) According to the $NCERT$ textbook,for normal fertility,at least $60\%$ of all sperms must have normal shape and size,and at least $40\%$ of them must show vigorous motility.
Therefore,the correct option is $D$.

(A) During the process of spermatogenesis,the developing spermatozoa are embedded in the $Sertoli$ cells.
$Sertoli$ cells are specialized somatic cells found within the seminiferous tubules of the testes.
Their primary function is to provide structural support,protection,and essential nutrients to the developing germ cells (spermatids) as they differentiate into mature spermatozoa.
Therefore,the correct option is $A$.

(C) $Sertoli$ cells are specialized somatic cells found within the seminiferous tubules of the mammalian testes.
These cells play a crucial role in spermatogenesis by providing structural and metabolic support to the developing germ cells.
They also form the blood-testis barrier,which protects developing sperm from the immune system.
Therefore,$Sertoli$ cells are characteristic of mammalian testes.

(D) Spermatogenesis is the process of formation of spermatozoa from spermatogonia.
It involves several stages: multiplication,growth,maturation,and spermiogenesis.
Spermiogenesis is the final stage of spermatogenesis where non-motile spermatids are transformed into mature,motile spermatozoa.
During this transformation,the Golgi apparatus of the spermatid develops into the acrosome,which covers the anterior portion of the nucleus.
Therefore,the formation of the acrosome occurs during the process of spermiogenesis.

(B) The germinal epithelium of the seminiferous tubules in the testes contains two types of cells: male germ cells (spermatogonia) and Sertoli cells.
Sertoli cells are also known as nurse cells or supporting cells.
Their primary function is to provide nutrition and structural support to the developing germ cells during spermatogenesis.
Leydig cells,on the other hand,are located in the interstitial spaces outside the seminiferous tubules and are responsible for the synthesis and secretion of androgens (testosterone).

(C) The process of ovulation is triggered by a sharp increase in the levels of $LH$ (Luteinizing Hormone) in the blood,which is known as the $LH$ surge.
This surge typically occurs around the middle of the menstrual cycle (approximately the $14^{th}$ day in a $28$-day cycle).
$LH$ acts on the mature Graafian follicle to induce the rupture of the follicle and the release of the secondary oocyte.
Therefore,$LH$ is the primary hormone responsible for inducing ovulation.

(C) In mammals,including rabbits,the sperm cells produced in the $Testis$ are immature and non-motile.
They are transported to the $Epididymis$,where they undergo physiological maturation,gaining motility and the ability to fertilize an egg.
Therefore,the $Epididymis$ is the site for the storage and maturation of sperm.

(B) The acrosome of a mammalian sperm contains hydrolytic enzymes that facilitate the penetration of the sperm into the egg.
These enzymes include Hyaluronidase,which digests the hyaluronic acid in the corona radiata,and Zona Lysin (also known as Acrosin),which helps in penetrating the zona pellucida.
Corona Penetrating Enzyme $(CPE)$ is also present.
Therefore,the combination of Hyaluronidase,$CPE$,and Zona Lysin is characteristic of the acrosomal content.

(C) After ovulation,the ruptured Graafian follicle transforms into a temporary endocrine structure called the $Corpus \ luteum$.
This structure secretes large amounts of progesterone,which is essential for the maintenance of the endometrium for potential implantation of the embryo.

(B) The human egg is classified as $Alecithal$ (or sometimes referred to as $Microlecithal$ in some contexts,but $Alecithal$ is the most precise term).
This means it contains a very negligible or almost no amount of yolk.
Since the human embryo receives nutrition directly from the mother through the placenta,there is no requirement for a large amount of stored yolk in the egg.

(D) Sustentacular cells,also known as $Sertoli$ cells,are located within the seminiferous tubules of the testes.
These cells provide nourishment to developing sperm and play a crucial role in the regulation of spermatogenesis.
When the rate of spermatogenesis is high,$Sertoli$ cells secrete a hormone called $Inhibin$.
$Inhibin$ acts on the anterior pituitary gland to inhibit the secretion of $FSH$ ($Follicle$ $Stimulating$ $Hormone$),thereby providing negative feedback to control and regulate the process of spermatogenesis.

(A) In the process of spermatogenesis,the $Spermatogonia$ (diploid,$2n$) undergo mitotic divisions to form $Primary$ $spermatocytes$ $(2n)$.
These $Primary$ $spermatocytes$ then undergo the first meiotic division $(Meiosis-I)$,which is a reductional division.
As a result of $Meiosis-I$,each $Primary$ $spermatocyte$ divides to form two haploid $(n)$ cells known as $Secondary$ $spermatocytes$.
Therefore,the correct option is $A$.

(B) The process of ovulation is triggered by a rapid surge in the levels of Luteinizing Hormone $(LH)$,commonly known as the $LH$ surge,which occurs mid-cycle (around the $14^{th}$ day of a $28$-day cycle).
Following ovulation,the remaining parts of the Graafian follicle transform into the corpus luteum under the influence of $LH$.
Therefore,$LH$ is responsible for both ovulation and the maintenance/development of the corpus luteum.

(B) The seminiferous tubules are the structural and functional units of the testes.
Inside the seminiferous tubules,the germinal epithelium consists of two types of cells: spermatogonia (male germ cells) and Sertoli cells (nurse cells).
Sertoli cells are large,pyramidal cells that are interspersed between the spermatogonia.
Their primary function is to provide nutrition and support to the developing germ cells during spermatogenesis.

(A) During the process of oogenesis,the primary oocyte undergoes unequal meiotic division.
This division results in the formation of a large haploid cell known as the secondary oocyte and a very small haploid cell known as the polar body.
The polar body contains very little cytoplasm and serves to discard the extra set of chromosomes,ensuring the secondary oocyte retains the majority of the nutrients and cytoplasm required for potential embryonic development.

(B) During gametogenesis,the second maturation phase involves Meiosis-$II$.
Meiosis-$II$ is known as an equational division because the number of chromosomes in the daughter cells remains the same as in the parent cell.
In this phase,the sister chromatids separate,resulting in the formation of haploid gametes from haploid secondary spermatocytes or oocytes.

(B) The human sperm was first observed and described by $Antonie \ van \ Leeuwenhoek$ in $1677$. He referred to them as 'animalcules' after observing them under a microscope.

(B) The process of release of spermatozoa from the seminiferous tubules into the lumen is known as $Spermiation$.
$Spermiogenesis$ is the transformation of spermatids into spermatozoa.
$Insemination$ is the transfer of sperm into the female reproductive tract.
$Ejaculation$ is the process of releasing semen from the male reproductive tract.

(C) During the process of oogenesis,the primary oocyte undergoes unequal meiotic division.
This division results in the formation of a large haploid cell called the secondary oocyte and a very small haploid cell known as the polar body.
The polar body contains very little cytoplasm and eventually degenerates.
Therefore,the small cells released during the maturation of the oocyte are called polar bodies.

(C) Gametogenesis is the biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. In humans,this process involves the formation of sperm (spermatogenesis) in males and ova (oogenesis) in females. Since both sperm and ova are haploid cells,the correct term for the product of gametogenesis is haploid gametes.

(B) Oligospermia is a medical condition characterized by a low sperm count in the semen.
According to the World Health Organization $(WHO)$ criteria,a normal sperm count is typically considered to be $20$ million or more sperm per milliliter of semen.
Therefore,a condition where the sperm count is less than $20$ million/ml is clinically defined as oligospermia.

(B) The acrosome is a cap-like structure present at the anterior end of the sperm head. It is formed during the process of spermiogenesis from the Golgi apparatus of the spermatid. The acrosome contains hydrolytic enzymes (such as hyaluronidase) that help in the penetration of the ovum during fertilization.

(A) The $LH$ (Luteinizing Hormone) is responsible for the ovulation of the Graafian follicle and the subsequent transformation of the ruptured follicle into the corpus luteum.
This process is known as luteinization.
Therefore,$LH$ stimulates the development and maintenance of the corpus luteum.

(D) The middle piece of the sperm contains numerous mitochondria.
These mitochondria produce energy in the form of $ATP$ (Adenosine Triphosphate).
This energy is essential for the motility of the sperm tail,which allows the sperm to swim through the female reproductive tract to reach and fertilize the ovum.

(C) Polar bodies are small haploid cells that are formed during oogenesis in females.
During the process of oogenesis,the primary oocyte undergoes meiosis $I$ to produce a large secondary oocyte and a small first polar body.
Subsequently,the secondary oocyte undergoes meiosis $II$ to produce a mature ovum (ootid) and a second polar body.
Therefore,the formation of polar bodies is a characteristic feature of oogenesis.

(C) Spermiogenesis is the final stage of spermatogenesis.
During this process,non-motile,spherical spermatids are transformed into mature,motile spermatozoa (sperms).
This transformation involves the formation of an acrosome,condensation of the nucleus,development of a flagellum,and reduction of cytoplasm.
Therefore,the correct process is the transformation of spermatids into spermatozoa.

(D) Fertilization is a specific interaction between the sperm and the ovum.
$1$. The surface of the ovum contains a chemical substance called fertilizin.
$2$. The surface of the sperm contains a complementary chemical substance called anti-fertilizin.
$3$. The interaction between fertilizin and anti-fertilizin is species-specific,ensuring that the sperm of one species fertilizes the ovum of the same species.
$4$. Therefore,anti-fertilizin is located on the surface of the sperm.

(C) The process by which primordial follicles develop into mature Graafian follicles is known as $Folliculogenesis$.
$Oogenesis$ refers to the production of the ovum itself.
$Luteinization$ is the process by which the ruptured follicle transforms into the corpus luteum after ovulation.
Therefore,the correct term for the formation of the Graafian follicle is $Folliculogenesis$.

(B) In a telolecithal egg,the yolk is very abundant and is concentrated at one pole,known as the vegetal pole. The cytoplasm and nucleus are restricted to the opposite pole,known as the animal pole. This type of egg is typically found in birds,reptiles,and some fishes.

(A) The process of release of the secondary oocyte (ovum) from the Graafian follicle of the ovary is known as ovulation. Upon release,the ovum is captured by the fimbriae of the fallopian tube (oviduct) and enters the ampulla region where fertilization typically occurs.

(C) In human gametogenesis,the ploidy of cells changes during meiosis.
$1$. Spermatogonia $(2n)$ and Oogonia $(2n)$ are diploid cells formed by mitosis.
$2$. Primary oocytes $(2n)$ are also diploid cells that undergo meiosis $I$.
$3$. Secondary spermatocytes $(n)$,secondary oocytes $(n)$,sperm $(n)$,and ova $(n)$ are all haploid cells formed after the completion of meiosis $I$ or $II$.
Therefore,Spermatogonia,Oogonia,and Primary oocytes are diploid.

(A) After the process of ovulation,the ruptured Graafian follicle undergoes a transformation. The remaining granulosa and theca cells proliferate and accumulate a yellow pigment called lutein. This structure is known as the $Corpus \ luteum$. It acts as an endocrine gland and secretes progesterone,which is essential for maintaining the endometrium during pregnancy.

(C) At $0^{\circ}C$ temperature,sperm do not die immediately but become inactive or enter a state of suspended animation.
This property is utilized in the process of cryopreservation,where sperm are stored at very low temperatures (often in liquid nitrogen at $-196^{\circ}C$) for long-term storage without losing their viability.
Therefore,at $0^{\circ}C$,they simply become inactive for some time.

(A) Spermatogenesis is the process of formation of sperms in the testes.
This process is regulated by the hypothalamic-pituitary-gonadal axis.
$GnRH$ (Gonadotropin-Releasing Hormone) from the hypothalamus stimulates the anterior pituitary to secrete $LH$ and $FSH$.
$LH$ acts on Leydig cells to stimulate the synthesis and secretion of androgens,which in turn stimulate the process of spermatogenesis.
Once spermatogenesis is initiated and maintained,the feedback mechanism involves the regulation of $GnRH$ levels to maintain hormonal balance.
However,in the context of physiological regulation,$GnRH$ is the primary hormone that initiates the cascade leading to spermatogenesis.

(A) Mammalian eggs are classified as $Alecithal$ (or $Microlecithal$ in some contexts) because they contain a negligible or very small amount of yolk. Since the embryo receives nourishment directly from the mother through the placenta,there is no need for a large yolk reserve.

(B) The $Antrum$ is a fluid-filled cavity that characterizes the mature $Graafian$ follicle in the ovary.
As the primary follicle develops into the secondary and then the tertiary follicle,the follicular cells proliferate and secrete fluid.
This fluid accumulates in a space called the $Antrum$,which is a hallmark feature of the tertiary follicle,also known as the $Graafian$ follicle.

(C) The acrosome is a cap-like structure present on the anterior portion of the sperm head.
It is derived from the Golgi apparatus and contains hydrolytic enzymes,collectively known as sperm lysins (e.g.,hyaluronidase).
These enzymes are released upon contact with the egg,facilitating the penetration of the sperm through the protective layers of the ovum (zona pellucida and corona radiata) during fertilization.
Therefore,the primary role of the acrosome is to assist in the penetration of the sperm into the ovum.

(B) The corpus luteum is a temporary endocrine structure in female mammals that is involved in the production of relatively high levels of progesterone and moderate levels of estradiol and inhibin $A$. It is formed from the ovarian follicle after ovulation. Therefore,it is found in the ovary.

(A) Sertoli cells are specialized somatic cells located within the seminiferous tubules of the testis.
They are often referred to as 'Nurse cells' because they provide structural and metabolic support to the developing germ cells (spermatids) during the process of spermatogenesis.
They also secrete factors that regulate spermatogenesis and form the blood-testis barrier.

(C) The germ hill,also known as the $cumulus \ oophorus$,is a cluster of follicular cells that surround the oocyte in a mature Graafian follicle.
It serves to protect the oocyte and facilitates its release during ovulation.
Therefore,it is specifically found within the Graafian follicle.

(D) In biological terms,a haploid cell contains a single set of chromosomes $(n)$.
$A$. Primary spermatocytes $(2n)$ and primary follicles $(2n)$ are diploid.
$B$. Secondary spermatocytes $(n)$ are haploid,but secondary follicles $(2n)$ are diploid.
$C$. Spermatogonia $(2n)$ and oogonia $(2n)$ are diploid.
$D$. Gametes (sperm and ovum) are haploid $(n)$ cells produced after meiosis. Therefore,the correct answer is $D$.

(B) The Graafian follicle is a mature ovarian follicle.
It consists of several layers, including the theca layers.
The $Theca \text{ } interna$ is the inner layer of the theca folliculi, which is highly vascularized and contains endocrine cells.
These cells are responsible for the secretion of the hormone estrogen (estradiol) under the influence of $LH$ (Luteinizing Hormone).
Therefore, the correct answer is $Theca \text{ } interna$.

(C) In the gonads of vertebrates,the production of germ cells (gametogenesis) involves two main processes:
$1$. Mitosis: The primordial germ cells undergo repeated mitotic divisions to increase their population and maintain a pool of stem cells (e.g.,spermatogonia or oogonia).
$2$. Meiosis: These cells then undergo meiosis to reduce the chromosome number by half,resulting in the formation of haploid gametes (sperm or ova).
Therefore,both mitosis and meiosis are essential for the production of functional germ cells.

(D) During spermiogenesis,the centrioles of the spermatid are involved in the formation of the sperm.
Specifically,the proximal centriole is located just behind the nucleus in the head region,while the distal centriole gives rise to the axial filament of the tail.
Since the question asks for the part formed from the centriole in a general context regarding the structural organization of the sperm,the tail (axial filament) is the primary motile structure derived from the distal centriole.

(A) During oogenesis in a human female,the primary oocyte undergoes meiosis $I$ to form one large secondary oocyte and one small first polar body.
Subsequently,the secondary oocyte undergoes meiosis $II$ only if fertilization occurs,resulting in one large ovum and one small second polar body.
If the first polar body also divides,it produces two additional polar bodies.
Thus,in total,$3$ polar bodies are typically produced during the complete process of oogenesis.

(A) The head of a mature sperm consists of a haploid nucleus and an acrosome.
The acrosome is a cap-like structure that covers the anterior portion of the nucleus and contains enzymes that help in the fertilization of the ovum.
The middle piece contains mitochondria,and the tail consists of an axial filament.